1. Field of the Invention
The present invention relates to an air intake apparatus for supplying intake air to a combustion chamber of an engine.
2. Description of the Related Art
FIG. 7 shows a schematic view of an air intake apparatus. As shown in FIG. 7, an air intake apparatus 100 includes an air intake duct 101, a resonator 110, an air cleaner 103, an air cleaner hose 104, a throttle body 105 and an intake manifold 106. The intake air is taken into the air intake duct 101 through an inlet 102, and supplied to a combustion chamber 109 of an engine through the resonator 110, the air cleaner 103, the air cleaner hose 104, the throttle body 105 and the intake manifold 106.
Noise leaking from the inlet 102 (hereinafter referred to as “intake noise”) becomes a problem in the air intake apparatus 100. The intake noise has a comparatively wide frequency band over 1 kHz. This frequency band is studded with a plurality of resonance peaks where the sound pressure level is conspicuously high. Therefore, the intake noise can be suppressed by reducing the resonance peaks.
For example, each resonance peak corresponds to a lower resonance mode corresponding to the tube length of the air intake duct 101, a lower resonance mode corresponding to the tube length of the air cleaner hose 104, or the like. Particularly a resonance peak in a comparatively low frequency band is generally called low-frequency booming noise. The low-frequency booming noise occurs in a comparatively low engine speed. The low-frequency booming noise is specially offensive to the ears of passengers in a vehicle cabin. Accordingly, to suppress the low-frequency booming noise is specially effective in silencing in the vehicle cabin. The low-frequency booming noise corresponds to the lower resonance mode corresponding to the whole length of the intake air passageway. Accordingly, in order to suppress the low-frequency booming noise, the pulsating pressure of the intake air in a portion where there is an antinode of the lower resonance mode corresponding to the whole length of the intake air passageway may be let out to the outside of the air intake apparatus.
Taking this point into consideration, Patent Document 1 discloses an air cleaner having an air-permeable member. FIG. 8 shows a schematic view of the air cleaner disclosed in the same document. Incidentally, portions similar to those in FIG. 7 are denoted by the same reference numerals correspondingly. As shown in FIG. 8, a part of a dirty-side bottom wall 111 of an air cleaner 103 is formed out of an air-permeable member 112. An antinode of a lower resonance mode corresponding to the whole length of an intake air passageway is located on the dirty side of the air cleaner 103. Thus, according to an air intake apparatus 100 disclosed in the same document, the pulsating pressure of the intake air can be let out from the inside of the air cleaner 103 to the outside thereof through the air-permeable member 112. It is therefore possible to suppress the low-frequency booming noise which is a low frequency component of the intake noise.
[Patent Document 1]
JP-2002-21660A
According to the air intake apparatus 100 disclosed in the same document, however, there is a fear that the noise increases instead due to the air-permeable member 112 in a comparatively high engine speed. That is, when the engine speed is high, there occurs no lower resonance mode corresponding to the whole length of the intake air passageway. In other words, when the engine speed is high, there occurs no low-frequency booming noise. It is therefore difficult to bring about the effect of suppressing the intake noise due to the air-permeable member 112.
In addition, noise having a resonance peak in another frequency band leaks from the inside of the air cleaner 103 to the outside thereof through the air-permeable member 112. In addition, there is also a fear that the air-permeable member 112 itself vibrates due to the pulsating pressure of the intake air, and serves as a source of noise. Thus, the noise leaking to the outside of the air intake apparatus 100 through the air-permeable member 112 (hereinafter referred to as “transmitted noise”) increases instead. In such a manner, according to the air intake apparatus 100 disclosed in the same document, there is a fear that the noise increases with the increase of the transmitted noise when the engine speed is comparatively high.